U.S. patent application number 15/581425 was filed with the patent office on 2017-08-10 for systems and methods for internal surface conditioning in plasma processing equipment.
This patent application is currently assigned to Applied Materials, Inc.. The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to Jiayin Huang, Nitin K. Ingle, Dmitry Lubomirsky, Soonam Park, Edwin C. Suarez, Yufei Zhu.
Application Number | 20170229293 15/581425 |
Document ID | / |
Family ID | 55655965 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170229293 |
Kind Code |
A1 |
Park; Soonam ; et
al. |
August 10, 2017 |
SYSTEMS AND METHODS FOR INTERNAL SURFACE CONDITIONING IN PLASMA
PROCESSING EQUIPMENT
Abstract
A method of conditioning internal surfaces of a plasma source
includes flowing first source gases into a plasma generation cavity
of the plasma source that is enclosed at least in part by the
internal surfaces. Upon transmitting power into the plasma
generation cavity, the first source gases ignite to form a first
plasma, producing first plasma products, portions of which adhere
to the internal surfaces. The method further includes flowing the
first plasma products out of the plasma generation cavity toward a
process chamber where a workpiece is processed by the first plasma
products, flowing second source gases into the plasma generation
cavity. Upon transmitting power into the plasma generation cavity,
the second source gases ignite to form a second plasma, producing
second plasma products that at least partially remove the portions
of the first plasma products from the internal surfaces.
Inventors: |
Park; Soonam; (Sunnyvale,
CA) ; Zhu; Yufei; (Sunnyvale, CA) ; Suarez;
Edwin C.; (Fremont, CA) ; Ingle; Nitin K.;
(San Jose, CA) ; Lubomirsky; Dmitry; (Cupertino,
CA) ; Huang; Jiayin; (Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
55655965 |
Appl. No.: |
15/581425 |
Filed: |
April 28, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15139243 |
Apr 26, 2016 |
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15581425 |
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14514213 |
Oct 14, 2014 |
9355922 |
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15139243 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 16/455 20130101;
H01L 21/31116 20130101; H01J 37/3255 20130101; C23C 16/45559
20130101; H01L 21/32137 20130101; C23C 16/50 20130101; H01J
37/32532 20130101; C23C 16/45536 20130101; H01J 37/32119 20130101;
H01L 22/26 20130101; H01L 21/67069 20130101; H01J 2237/334
20130101; C23C 16/505 20130101; H01L 21/67253 20130101; H01J
37/32082 20130101; C23C 16/52 20130101; H01J 37/32623 20130101;
H01J 37/32357 20130101; H01J 37/32972 20130101; H01J 37/3244
20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01L 21/3213 20060101 H01L021/3213; C23C 16/455
20060101 C23C016/455; H01L 21/66 20060101 H01L021/66; C23C 16/505
20060101 C23C016/505; C23C 16/52 20060101 C23C016/52; H01L 21/311
20060101 H01L021/311; H01L 21/67 20060101 H01L021/67 |
Claims
1. A plasma processing system, comprising: a remote plasma system
for ionizing first source gases; and a processing chamber
comprising: a plasma generation cavity that is bounded by: a first
planar electrode that is configured for transfer of the ionized
first source gases and second plasma source gases into the plasma
generation cavity through first perforations therein, a second
planar electrode that is configured with perforations configured
for transfer of plasma products from the plasma generation cavity
toward a processing region, and a ring shaped insulator that is
disposed about and in contact with a periphery of the first
electrode, and about and in contact with a periphery of the second
electrode; and a power supply that provides electrical power across
the first and second planar electrodes to ignite a plasma with the
ionized first source gases and the second plasma source gases in
the plasma generation cavity, to produce the plasma products;
wherein: one of the first electrode, the second electrode, and the
insulator includes a port that provides an optical signal from the
plasma, the port being disposed and oriented such that the optical
signal is not influenced by interactions of the plasma products
after they transfer through the second electrode toward the
processing region.
2. The plasma processing system of claim 1, the processing chamber
further comprising a planar diffuser between the second planar
electrode and the plasma generation cavity, configured to allow the
plasma products to transfer from the second planar electrode,
through perforations of the diffuser, into the processing
region.
3. The plasma processing system of claim 2, the planar diffuser
forms gas channels having outlets only on a processing region side
thereof, the outlets being interspersed with the perforations, such
that an additional gas from the outlets can mix with the plasma
products as the plasma products enter the processing region.
4. The plasma processing system of claim 1, wherein the first
electrode includes the port providing an optical signal from the
plasma.
5. The plasma processing system of claim 1, wherein the second
electrode includes the port providing an optical signal from the
plasma.
6. The plasma processing system of claim 1, wherein the insulator
includes the port providing an optical signal from the plasma.
7. The plasma system of claim 6, wherein the insulator comprises a
ceramic ring forming a radial aperture for transmission of optical
emissions from the plasma, and the port comprises: an optical
window that is sealable to the ceramic ring across an outer opening
of the radial aperture, and a fixture that positions a fiber optic
adjacent the optical window such that the optical emissions
propagate into the fiber optic to form the optical signal.
8. The plasma system of claim 7, wherein the optical window
comprises sapphire or quartz.
9. The plasma system of claim 1, further comprising an optical
emission spectrometer that receives the optical signal and
generates emission peak data from the optical signal.
10. The plasma system of claim 9, further comprising a computer
configured for generating records of the emission peak data.
11. The plasma system of claim 10, the emission peak data including
hydrogen emission peak data, the computer being configured to
calculate a stability metric of the hydrogen emission peak data
over sequential process sequences of the plasma source.
12. The plasma system of claim 1, wherein at least one of the first
and second electrodes comprises yttria.
13. The plasma system of claim 1, further comprising an optical
probe that is disposed adjacent the plasma generation cavity and is
oriented such that captured optical emissions are not affected by
interaction of the plasma with a workpiece.
14. A plasma processing system comprising: a processing chamber
comprising a plurality of electrodes and one or more internal
surfaces; a plasma generation cavity bounded at least in part by
one or more internal surfaces; a power source configured to apply
power across the electrodes to ignite a plasma of plasma source
gases within the plasma generation cavity; an optical probe that is
disposed adjacent the plasma generation cavity and is oriented such
that captured optical emissions are not affected by interaction of
the plasma with a workpiece, wherein the optical probe is
configured to capture optical emissions from the plasma; and a
computer system configured to monitor one or more emission peaks of
the captured optical emissions to assess the surface conditioning
of the one or more internal surfaces.
15. The plasma processing system of claim 14, where the computer
system is configured to generate a record of at least a subset of
the captured optical emissions each time an etch recipe reaches a
predetermined recipe step.
16. The plasma processing system of claim 15, wherein the computer
system is further configured to calculate a stability metric from
the records generated each time the etch recipe reaches the
predetermined recipe step over a plurality of recipe cycles, and
wherein the computer system is configured to compare a stability
metric with a predetermined criterion to assess the surface
conditioning of the one or more internal surfaces.
17. The plasma processing system of claim 15, wherein the optical
probe is a first optical probe, wherein the plasma processing
system further comprises a second optical probe configured to
monitor optical emissions that are affected by interaction of the
plasma with the workpiece, wherein the second optical probe is
coupled with an endpoint detector configured to control the etch
recipe responsive to emissions captured by the second optical
probe.
18. The plasma processing system of claim 14, further comprising an
insulator including a port with which the optical probe is
coupled.
19. The plasma processing system of claim 18, wherein the insulator
comprises a ceramic ring forming a radial aperture for transmission
of optical emissions from the plasma, and the port comprises: an
optical window that is sealable to the ceramic ring across an outer
opening of the radial aperture, and a fixture that positions a
fiber optic adjacent the optical window such that the optical
emissions propagate into the fiber optic to form an optical
signal.
20. The plasma processing system of claim 19, wherein the optical
window comprises sapphire or quartz.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/139,243, filed Apr. 26, 2016, which is a
continuation of U.S. patent application Ser. No. 14/514,213, filed
Oct. 14, 2014, the entire disclosures of which are incorporated by
reference herein for all purposes.
TECHNICAL FIELD
[0002] The present disclosure applies broadly to the field of
plasma processing equipment. More specifically, systems and methods
for internal surface conditioning of a plasma generator using
optical emission spectroscopy are disclosed.
BACKGROUND
[0003] Semiconductor processing often utilizes plasma processing to
etch, clean or deposit material on semiconductor wafers.
Predictable and reproducible wafer processing is facilitated by
plasma processing parameters that are stable and well controlled.
Certain changes to equipment and/or materials involved in plasma
processing can temporarily disrupt stability of plasma processing.
This typically occurs when such changes affect the surface
chemistry of plasma system components, as compared to the surface
chemistry that results from long term use in a single process. For
example, plasma chamber components may require conditioning upon
first-time use, or after the chamber is vented to atmospheric air.
In such cases, a plasma process may initially exhibit deliverables
such as etch rate, etch selectivity or deposition rate that vary
but may stabilize over time, for example as surface coatings within
the process chamber come into equilibrium with the plasma process
conditions. Semiconductor manufacturers value rapid stabilization
of process conditions and reliable confirmation of process
stability, so that a new or repaired plasma chamber can be placed
into use as soon as possible.
SUMMARY
[0004] In an embodiment, a plasma source includes a first
electrode, configured for transfer of one or more plasma source
gases through first perforations therein; an insulator, disposed in
contact with the first electrode about a periphery of the first
electrode; and a second electrode, disposed with a periphery of the
second electrode against the insulator such that the first and
second electrodes and the insulator define a plasma generation
cavity. The second electrode is configured for movement of plasma
products from the plasma generation cavity therethrough toward a
process gas chamber. A power supply provides electrical power
across the first and second electrodes to ignite a plasma with the
one or more plasma source gases in the plasma generation cavity to
produce the plasma products. One of the first electrode, the second
electrode and the insulator includes a port that provides an
optical signal from the plasma.
[0005] In an embodiment, a method assesses surface conditioning of
one or more internal surfaces of a plasma processing system. The
method includes introducing one or more plasma source gases within
a plasma generation cavity of the plasma processing system, the
plasma generation cavity being bounded at least in part by the one
or more internal surfaces, and applying power across electrodes of
the plasma processing system to ignite a plasma with the plasma
source gases within the plasma generation cavity. Optical emissions
from the plasma are captured with an optical probe that is disposed
adjacent the plasma generation cavity and is oriented such that the
captured optical emissions are not affected by interaction of the
plasma with a workpiece. One or more emission peaks of the captured
optical emissions are monitored to assess the surface conditioning
of the one or more internal surfaces.
[0006] In an embodiment, a plasma processing system includes a
remote plasma system for ionizing first source gases, and two
processing units, each of the two processing units configured to
receive at least the ionized first source gases from the remote
processing system, and second source gases. Each of the processing
units includes a plasma generation chamber that is bounded by a
first planar electrode that is configured for transfer of the
ionized first source gases and the second plasma source gases into
the plasma generation chamber through first perforations therein, a
second planar electrode that is configured with perforations
configured for transfer of plasma products from the plasma
generation cavity toward a process chamber, and a ring shaped
insulator that is disposed about and in contact with a periphery of
the first electrode, and about and in contact with a periphery of
the second electrode. Each of the processing units further includes
a power supply that provides electrical power across the first and
second planar electrodes to ignite a plasma with the ionized first
source gases and the second plasma source gases in the plasma
generation cavity, to produce the plasma products. One of the first
electrode, the second electrode and the insulator includes a port
that provides an optical signal from the plasma. The port is
disposed and oriented such that the optical signal is not
influenced by interactions of the plasma products after they
transfer through the second electrode toward the process
chamber.
[0007] In an embodiment, a method of conditioning internal surfaces
of a plasma source includes flowing first source gases into a
plasma generation cavity of the plasma source that is enclosed at
least in part by the internal surfaces. Upon transmitting power
into the plasma generation cavity, the first source gases ignite to
form a first plasma, producing first plasma products, portions of
which adhere to the internal surfaces. The method further includes
flowing the first plasma products out of the plasma generation
cavity toward a process chamber where a workpiece is processed by
the first plasma products, flowing second source gases into the
plasma generation cavity. Upon transmitting power into the plasma
generation cavity, the second source gases ignite to form a second
plasma, producing second plasma products that at least partially
remove the portions of the first plasma products from the internal
surfaces.
[0008] In an embodiment, a method of conditioning one or more
internal surfaces of a plasma source after the internal surfaces
are exposed to atmospheric air includes flowing at least a
hydrogen-containing gas into a plasma generation cavity of the
plasma source, the plasma generation cavity being enclosed at least
in part by the one or more internal surfaces, transmitting power
into the plasma generation cavity to generate a hydrogen-containing
plasma, such that H radicals remove excess oxygen from the internal
surfaces, and monitoring emission peaks of the plasma until the
emission peaks are stable.
[0009] In an embodiment, a method of maintaining stability of a
process attribute of a plasma processing system that etches
material from wafers includes generating an etch plasma within the
plasma processing system to create etch plasma products, wherein
portions of the etch plasma products adhere to one or more internal
surfaces of the plasma processing system, using the etch plasma
products to etch the material from the one of the wafers, wherein
the portions of the etch plasma products adhered to the one or more
internal surfaces affect the process attribute, and generating a
conditioning plasma within the plasma processing system to create
conditioning plasma products, wherein the conditioning plasma
products remove at least some of the etch plasma products adhered
to the one or more internal surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present disclosure may be understood by reference to the
following detailed description taken in conjunction with the
drawings briefly described below, wherein like reference numerals
are used throughout the several drawings to refer to similar
components. It is noted that, for purposes of illustrative clarity,
certain elements in the drawings may not be drawn to scale. In
instances where multiple instances of an item are shown, only some
of the instances may be labeled, for clarity of illustration.
[0011] FIG. 1 schematically illustrates major elements of a plasma
processing system, according to an embodiment.
[0012] FIG. 2 schematically illustrates major elements of a plasma
processing system, in a cross-sectional view, according to an
embodiment.
[0013] FIG. 3 schematically illustrates details of region A shown
in FIG. 2.
[0014] FIG. 4 schematically illustrates a top plan view of an
exemplary plasma processing system configured to perform various
types of processing operations, according to an embodiment.
[0015] FIG. 5 schematically illustrates a pair of processing
chambers, disposed as a tandem pair of processing chambers with a
tandem tray, according to an embodiment.
[0016] FIG. 6 is a flowchart illustrating a method for assessing
surface conditioning of one or more internal surfaces of a plasma
processing system, according to an embodiment.
[0017] FIGS. 7A and 7B illustrate emission peak information
obtained by using the method illustrated in FIG. 6, with apparatus
like that shown in FIGS. 2 and 3, according to an embodiment.
[0018] FIGS. 8A and 8B show plots of emission peak intensities
measured in a plasma chamber, over time, for a hydrogen peak and
for fluorine peaks, according to an embodiment.
[0019] FIG. 9 is a plot of selected ones of the hydrogen emission
peaks from FIG. 8A, and etch rate measurements taken at the
corresponding times as the selected hydrogen emission peaks,
according to an embodiment.
[0020] FIG. 10A illustrates a yttria surface that is devoid of
hydrogen, according to an embodiment.
[0021] FIG. 10B illustrates the yttria surface of FIG. 10A, with a
few H radicals adhered to the surface through dangling bonds,
according to an embodiment.
[0022] FIG. 10C illustrates the yttria surface of FIG. 10B, with F
radicals reacting with some of the H radicals, according to an
embodiment.
[0023] FIG. 11 is a flowchart that illustrates an etch recipe that
alternates etching on a workpiece, with a conditioning step,
according to an embodiment.
[0024] FIG. 12A illustrates a yttria surface with a few F atoms
adhered to the surface through dangling bonds, according to an
embodiment.
[0025] FIG. 12B illustrates a yttria surface undergoing a reaction
to remove fluorine, according to an embodiment.
[0026] FIG. 13A illustrates a yttria surface with adsorbed
fluorine, reacting with moisture to form YO.sub.2 in solid form,
and HF which is carried away in gas form, according to an
embodiment.
[0027] FIG. 13B illustrates the yttria surface of FIG. 13A, with an
oxygen atom of YO.sub.2 in solid form reacting with H radicals to
form H.sub.2O, which is carried away in vapor form, according to an
embodiment.
DETAILED DESCRIPTION
[0028] FIG. 1 schematically illustrates major elements of a plasma
processing system 100, according to an embodiment. System 100 is
depicted as a single wafer, semiconductor wafer plasma processing
system, but it will be apparent to one skilled in the art that the
techniques and principles herein are applicable to plasma
generation systems of any type (e.g., systems that do not
necessarily process wafers or semiconductors). Processing system
100 includes a housing 110 for a wafer interface 115, a user
interface 120, a plasma processing unit 130, a controller 140 and
one or more power supplies 150. Processing system 100 is supported
by various utilities that may include gas(es) 155, external power
170, vacuum 160 and optionally others. Internal plumbing and
electrical connections within processing system 100 are not shown,
for clarity of illustration.
[0029] Processing system 100 is shown as a so-called indirect, or
remote, plasma processing system that generates a plasma in a first
location and directs the plasma and/or plasma products (e.g., ions,
molecular fragments, energized species and the like) to a second
location where processing occurs. Thus, in FIG. 1, plasma
processing unit 130 includes a remote plasma source 132 that
supplies plasma and/or plasma products for a process chamber 134.
Process chamber 134 includes one or more wafer pedestals 135, upon
which wafer interface 115 places a workpiece 50 (e.g., a
semiconductor wafer, but could be a different type of workpiece)
for processing. In operation, gas(es) 155 are introduced into
plasma source 132 and a radio frequency generator (RF Gen) 165
supplies power to ignite a plasma within plasma source 132. Plasma
and/or plasma products pass from plasma source 132 through a
diffuser plate 137 to process chamber 134, where workpiece 50 is
processed.
[0030] Although an indirect plasma processing system is illustrated
in FIG. 1 and elsewhere in this disclosure, it should be clear to
one skilled in the art that the techniques, apparatus and methods
disclosed herein are equally applicable to direct plasma processing
systems--e.g., where a plasma is ignited at the location of the
workpiece(s). Similarly, in embodiments, the components of
processing system 100 may be reorganized, redistributed and/or
duplicated, for example: (1) to provide a single processing system
with multiple process chambers; (2) to provide multiple remote
plasma sources for a single process chamber; (3) to provide
multiple workpiece fixtures (e.g., wafer pedestals 135) within a
single process chamber; (4) to utilize a single remote plasma
source to supply plasma products to multiple process chambers;
and/or (5) to provide plasma and gas sources in serial/parallel
combinations such that various source gases may be ionized zero,
one, two or more times, and mixed with other source gases before or
after they enter a process chamber, and the like.
[0031] Plasma-Only Monitoring with OES
[0032] FIG. 2 schematically illustrates major elements of a plasma
processing system 200, in a cross-sectional view, according to an
embodiment. Plasma processing system 200 is an example of plasma
processing unit 130, FIG. 1. Plasma processing system 200 includes
a process chamber 205 and a plasma source 210. As shown in FIG. 2,
plasma source 210 introduces gases 155(1) directly, and/or gases
155(2) that are ionized by an upstream remote plasma source 202, as
plasma source gases 212, through an RF electrode 215. RF electrode
215 includes (e.g., is electrically tied to) a first gas diffuser
220 and a faceplate 225 that serve to redirect flow of the source
gases so that gas flow is uniform across plasma source 210, as
indicated by arrows 231. After flowing through face plate 225, an
insulator 230 electrically insulates RF electrode 215 from a
diffuser 235 that is held at electrical ground (e.g., diffuser 235
serves as a second electrode counterfacing face plate 225 of RF
electrode 215). Surfaces of RF electrode 215, diffuser 235 and
insulator 230 define a plasma generation cavity (see plasma
generation cavity 240, FIG. 3) where a plasma 245 is created when
the source gases are present and RF energy is provided through RF
electrode 215. RF electrode 215 and diffuser 235 may be formed of
any conductor, and in embodiments are formed of aluminum (or an
aluminum alloy, such as the known "6061" alloy type). Surfaces of
face plate 225 and diffuser 235 that face the plasma cavity or are
otherwise exposed to reactive gases may be coated with yttria
(Y.sub.2O.sub.3) or alumina (Al.sub.2O.sub.3) for resistance to the
reactive gases and plasma products generated in the plasma cavity.
Insulator 230 may be any insulator, and in embodiments is formed of
ceramic. A region denoted as A in FIG. 2 is shown in greater detail
in FIG. 3. Emissions from plasma 245 enter a fiber optic 270 and
are analyzed in an optical emission spectrometer ("OES") 280, as
discussed further below.
[0033] Plasma products generated in plasma 245 pass through
diffuser 235 that again helps to promote the uniform distribution
of plasma products, and may assist in electron temperature control.
Upon passing through diffuser 235, the plasma products pass through
a further diffuser 260 that promotes uniformity as indicated by
small arrows 227, and enter process chamber 205 where they interact
with workpiece 50, such as a semiconductor wafer, atop wafer
pedestal 135. Diffuser 260 includes further gas channels 250 that
may be used to introduce one or more further gases 155(3) to the
plasma products as they enter process chamber 205, as indicated by
very small arrows 229.
[0034] Embodiments herein may be rearranged and may form a variety
of shapes. For example, RF electrode 215 and diffuser 235 are
substantially radially symmetric in the embodiment shown in FIG. 2,
and insulator 230 is a ring with upper and lower planar surfaces
that are disposed against peripheral areas of face plate 225 and
diffuser 235, for an application that processes a circular
semiconductor wafer as workpiece 50. However, such features may be
of any shape that is consistent with use as a plasma source.
Moreover, the exact number and placement of features for
introducing and distributing gases and/or plasma products, such as
diffusers, face plates and the like, may also vary. Also, in a
similar manner to diffuser 260 including gas channels 250 to add
gas 155(3) to plasma products from plasma 245 as they enter process
chamber 205, other components of plasma processing system 200 may
be configured to add or mix gases 155 with other gases and/or
plasma products as they make their way through the system to
process chamber 205.
[0035] FIG. 3 schematically illustrates details of region A shown
in FIG. 2. Face plate 225, insulator 230 and diffuser 235 seal to
one another such that a plasma generation cavity 240 that is
bounded by face plate 225, insulator 230 and diffuser 235 can be
evacuated. A facing surface 226 of face plate 225, and/or a facing
surface 236 of diffuser 235 may be coated with yttria
(Y.sub.2O.sub.3) or alumina (Al.sub.2O.sub.3) for resistance to the
gases and/or plasmas to be used.
[0036] When plasma source gases are introduced and electrical power
is provided across face plate 225 and diffuser 235, a plasma 245
can form therein. Insulator 230 forms a radial aperture 237; an
optical window 310 seals to insulator 230 over aperture 237.
Optical window 310 is formed of sapphire, however it is appreciated
that other materials for optical window 310 may be selected based
on resistance to plasma source gases and/or plasma products of
plasma 245, or transmissivity to optical emissions, as discussed
below. In the embodiment shown in FIG. 3, an o-ring 340 seats in
recesses 345 to facilitate sealing optical window 310 to insulator
230; however, other sealing geometries and methods may be utilized.
In embodiments, plasma generation cavity 240 is evacuated such that
atmospheric pressure (external to plasma generation cavity 240)
assists in sealing components such as optical window 310 to
insulator 230.
[0037] Fiber optic 270 is positioned such that when plasma 245
exists in plasma generation cavity 240, optical emissions 350
originate in plasma 245, propagate through radial aperture 237 and
optical window 310, and into fiber optic 270 to generate an optical
signal therein. Fiber optic 270 transmits optical emissions 350 to
OES 280, FIG. 2. In embodiments, fiber optic 270 is a 400 .mu.m
core optical fiber; however, other core sizes and various fiber
materials may be selected for transmissivity of optical emissions
350 and to manage signal strength within fiber optic 270. For
example, plasmas 245 that generate low levels of optical emissions
350 may be monitored utilizing a relatively wide core (e.g., 400
.mu.m) fiber optic 270, while plasmas that generate higher levels
of optical emissions 350 may be monitored utilizing relatively
narrower cores (e.g., 110 .mu.m, 100 .mu.m, 62.5 .mu.m, 50 .mu.m, 9
.mu.m or other core sizes) in order to limit the optical signal
reaching OES 280. One or more filters may be utilized at OES 280 to
absorb stray light and/or emissions that are not within a spectral
band of interest.
[0038] OES 280 analyzes the optical signal received from fiber
optic 270 to identify emission peaks within the signal, including
identifying specific emission peaks as corresponding to energy
transitions of specific elements. In some embodiments, spectra
and/or information characterizing emission peaks therein may be
viewed and/or manipulated on OES 280. In some of these and in other
embodiments, emission peak information may be transferred to a
computer 290 for analysis, manipulation, storage and/or
display.
[0039] In embodiments, a fiber optic connector 330 terminates fiber
optic 270, and a block 320 positions fiber optic connector 330 with
respect to optical window 310, as shown in FIG. 3. However, this
arrangement is by way of example only; other embodiments may
provide a custom termination of fiber optic 270 that does not
involve a connector 330, and various arrangements for positioning
fiber optic 270 and/or connector 330 with respect to window 310 may
be implemented in place of block 320. When utilized, block 320 may
extend in and out of the cross-sectional plane shown in FIG. 3 to
form attachment regions, and may fasten to insulator 230 using
fasteners such as screws in such regions. Block 320 and/or screws
that attach block 320 to insulator 230 are advantageously
fabricated of insulative materials such as plastic or ceramic, to
mitigate any possibility of electrical arcing to or from face plate
225 and diffuser 235, and/or other structures.
[0040] It is appreciated that aperture 237 and optical window 310,
at least, function as a port for providing an optical signal from
plasma 245 that can be utilized to monitor aspects of plasma source
210. It is also appreciated that such port may be provided at a
variety of locations within a plasma source. For example, generally
speaking, a capacitively coupled plasma source will include at
least two electrodes separated by an insulator; a port such as
described above could be disposed with any of the electrodes or the
insulator. Similarly, an inductively coupled plasma source (or any
other type of plasma source) could include a port disposed with any
vessel in which the plasma is initially generated. Materials and/or
locations of such ports should be selected so as not to disrupt
electrical or magnetic circuits that are important to the plasma
source (e.g., to mitigate arcing and/or disturbance of magnetic
field distributions, for inductively coupled plasma sources).
[0041] Returning to FIG. 2, optical monitoring of plasma at the
place where it is generated in a remote plasma source provides
unique benefits. Because plasma 245 is monitored upstream of its
interactions with a workpiece 50 (e.g., a wafer), the monitoring
provides characterization of the plasma source alone, which may be
contrasted or correlated with effects produced by interaction with
the workpiece. That is, the geometry of insulator 230 and radial
aperture 237 will tend to provide fiber optic 270 with an effective
"view" that is limited to optical emissions resulting from plasma
245 and interactions of those emissions with adjacent surfaces,
rather than emissions resulting from downstream interactions and/or
direct views of surfaces within a process chamber. Monitoring of a
plasma at a location where it has not yet had an opportunity to
interact with a workpiece is called "upstream" plasma monitoring
herein.
[0042] By way of contrast, optical monitoring of workpieces
themselves, and/or plasma interaction with such workpieces, may be
used to monitor certain plasma effects on the workpiece, but are
susceptible to influence by the workpiece. Workpiece-affected
plasma characteristics, including optical emissions captured with
optical probes, are sometimes utilized to determine a plasma
processing endpoint, that is, to identify a time at which
processing is essentially complete such that some aspect of the
plasma process can be turned off. For example, interaction with a
workpiece can affect a plasma by releasing reaction products from
the workpiece, and/or the workpiece can deplete reactive species
from the plasma. When reaction products from the workpiece are no
longer detected, it may signify that a layer to be etched has
"cleared" such that etch gases and/or RF energy can be turned off.
However, such optical probes are situated where the optical
emissions that are captured are affected by the workpiece.
[0043] Both workpiece-affected and upstream plasma monitoring can
be useful tools in determining whether variations in processed
workpieces are due to variations in a plasma as generated, or due
to variations present in the workpieces before they interact with
the plasma. In certain embodiments herein, stable process results
correlate strongly with upstream plasma monitoring results.
Specifically, process results have been found to correlate with
certain emission peaks measured with the apparatus described in
connection with FIGS. 2 and 3. When strong correlations between
upstream monitoring of plasma emission peaks and process results
can be identified, it becomes possible, in embodiments, to run
conditioning process cycles without exposing valuable workpieces to
risk until those emission peaks are observed to be stable. Once the
emission peaks are stable, workpieces can be processed in
confidence that the process results will be as expected.
[0044] Stability in emission peaks obtained from upstream
monitoring can indicate equilibrium in reactions between the
generated plasma and adjacent surfaces. For example, certain
surfaces of electrodes, diffusers and the like may interact with a
plasma to slowly give off, or absorb, certain elements that are
important to process results, such that the resulting plasma
process will not be stable until the surfaces are in equilibrium
with the plasma. In embodiments, electrodes, diffusers and the like
may be coated with refractory materials such as yttria
(Y.sub.2O.sub.3) or alumina (Al.sub.2O.sub.3) for resistance to the
gases and/or plasmas to be used. These materials can interact with
plasma products such as free hydrogen, such that plasmas generated
around such surfaces may not be stable until the surfaces are
either saturated or substantially depleted of hydrogen. In either
case, emission peaks generated through upstream plasma monitoring
can be useful for assessing plasma stability.
[0045] Accurately identifying when plasma equipment is running a
stable process is valuable in the semiconductor industry.
Semiconductor processing is characterized both by unusable
equipment having high cost and workpieces having high value that is
at risk if processing is not optimal. For example, a single plasma
processing system may represent hundreds of thousands, or a few
million dollars of capital investment, with output of a
multimillion dollar wafer fabrication area being dependent on only
a few of such systems. Yet, a single semiconductor wafer may accrue
hundreds or thousands of dollars of invested processing costs, and
a piece of plasma equipment might process tens of such wafers per
hour. Thus the financial costs of equipment downtime, or of
utilizing equipment that is not operating correctly, are both quite
high.
[0046] FIG. 4 schematically illustrates a top plan view of an
exemplary plasma processing system 400A configured to perform
various types of processing operations. In FIG. 4, a pair of front
opening unified pods ("FOUPs") or holding chambers 402 supply
workpieces (e.g., semiconductor wafers) of a variety of sizes that
are received by robotic arms 404 and placed into low pressure
loading chambers 406 before being placed into one of the workpiece
processing chambers 408a-f, positioned on tandem trays 409a-c. In
alternative arrangements, the system 400A may have additional
FOUPs, and may for example have 3, 4, 5, 6, etc. or more FOUPs. The
process chambers may include any of the chambers as described
elsewhere in this disclosure. Robotic arms 411 may be used to
transport the workpieces from the loading chambers 406 to the
workpiece processing chambers 408a-f and back through a transfer
chamber 410. Two loading chambers 406 are illustrated, but the
system may include a plurality of loading chambers that are each
configured to receive workpieces into a vacuum environment for
processing. Process chambers 408 and transfer chamber 410 may be
maintained in an inert environment, such as with nitrogen purging,
which may be continuously flowed through each of the chambers to
maintain the inert atmosphere. The loading chamber 406 may
similarly be configured to be purged with nitrogen after receiving
a workpiece in order to provide the workpiece to the process
sections in a similar environment.
[0047] Each workpiece processing chamber 408a-f, can be outfitted
to perform one or more workpiece processing operations including
dry etch processes, cyclical layer deposition (CLD), atomic layer
deposition (ALD), chemical vapor deposition (CVD), physical vapor
deposition (PVD), etch, pre-clean, degas, orientation, and other
workpiece processes. In a disclosed embodiment, for example, the
system may include at least two pairs of tandem processing
chambers. A first of the at least two pairs of tandem processing
chambers may be configured to perform a silicon oxide etching
operation, and the second of the at least two pairs of tandem
processing chambers may be configured to perform a silicon or
silicon nitride etching operation. A given pair of processing
chambers 408 may both be configured for a specific process step,
and monitored using methods described herein to ensure that the
processing provided by each of the pair of chambers matches closely
to the other. When configured in pairs, each processing chamber 408
may be coupled independently with support equipment such as gas
supplies, RF generators, remote plasma generators and the like, but
in embodiments, adjacent processing chambers 408 share connections
with certain such support equipment.
[0048] The workpiece processing chambers 408a-f may include one or
more system components for depositing, annealing, curing and/or
etching a film on the workpiece. In one configuration, two pairs of
the processing chambers, e.g., 408c-d and 408e-f, may be used to
perform a first etching operation on the workpiece, and the third
pair of processing chambers, e.g., 408a-b, may be used to perform a
second etching operation on the workpiece. In another
configuration, all three pairs of chambers, e.g., 408a-f, may be
configured to etch a dielectric film on the workpiece. In still
another configuration, a first pair of the processing chambers,
e.g., 408a-b, may perform a deposition operation, such as
depositing a flowable film, a native oxide, or additional
materials. A second pair of the processing chambers, e.g., 408c-d,
may perform a first etching operation, and the third pair of the
processing chambers, e.g., 408e-f, may perform a second etching
operation. Any one or more of the processes described may be
alternatively carried out in chambers separated from the
fabrication system shown in different embodiments. It will be
appreciated that additional configurations of deposition, etching,
annealing, and curing chambers for films are contemplated by system
400A.
[0049] The processing chambers herein may perform any number of
processes, such as a PVD, a CVD (e.g., dielectric CVD, MCVD, MOCVD,
EPI), an ALD, a decoupled plasma nitridation (DPN), a rapid thermal
processing (RTP), or a dry-etch process to form various device
features on a surface of a workpiece. The various device features
may include, but are not limited to the formation and/or etching of
interlayer dielectric layers, gate dielectric layers,
polycrystalline silicon ("polysilicon") layers or gates, forming
vias and trenches, planarization steps, and depositing contact or
via level interconnects. In one embodiment, certain positions may
be occupied by service chambers that are adapted for degassing,
orientation, cool down, analysis and the like. For example, one
chamber may include a metrology chamber that is adapted to perform
a preparation/analysis step and/or a post-processing/analysis step
to analyze a property of the workpiece before or after performing a
processing step in a processing sequence. In general, the
properties of the workpiece that can be measured in the metrology
chamber may include, but are not limited to, a measurement of
intrinsic or extrinsic stress in one or more layers deposited on a
surface of the workpiece, film composition of one or more deposited
layers, a number of particles on the surface of the workpiece,
and/or a thickness of one or more layers found on the surface of
the workpiece. Data collected from the metrology chamber may then
be used by a system controller to adjust one or more process
variables in one or more of the processing steps to produce
favorable process results on subsequently processed workpieces.
[0050] System 400A may include additional chambers 405, 407 on
opposite sides of an interface section 403. The interface section
403 may include at least two interface transfer devices, such as
robot arms 404, that are configured to deliver workpieces between
FOUPs 402 and the plurality of loading chambers 406. The holding
chambers 402 may be coupled with the interface section 403 at a
first location of the interface section, and the loading chambers
may be coupled with the interface section 403 at a second location
of the interface section 403 that is opposite the plurality of
holding chambers 402. The additional chambers may be accessed by
interface robot arms 404, and may be configured for transferring
workpieces through interface section 403. For example, chamber 405
may provide, for example, wet etching capabilities and may be
accessed by interface robot arm 404a through the side of interface
section 403. The wet station may be coupled with interface section
403 at a third location of interface section 403 between the first
location and second location of the interface section. In disclosed
embodiments the third location may be adjacent to either of the
first and second locations of interface section 403. Additionally,
chamber 407 may provide, for example, additional storage and may be
accessed by interface robot arm 404b through the opposite side of
interface section 403 from chamber 405. Chamber 407 may be coupled
with interface section 403 at a fourth location of the interface
section opposite the third location. Interface section 403 may
include additional structures for allowing the transfer of
workpieces between the robot arms 404, including transfer section
412 positioned between the robot arms 404. Transfer section 412 may
be configured to hold one or more workpieces, and may be configured
to hold 2, 5, 10, 15, 20, 25, 50, 100 etc. or more workpieces at
any given time for delivery for processing. A transfer section 412
may include additional capabilities including cooling of the
workpieces below atmospheric conditions as well as atmospheric
cleaning of the wafers, for example. The system 400A may
additionally include gas delivery systems and system controllers
(not shown) for providing precursors and instructions for
performing a variety of processing operations.
[0051] FIG. 5 is a schematic side view illustrating a pair of
processing chambers 408g and 408h, disposed as a tandem pair of
processing chambers with a tandem tray 409. Each processing chamber
408g, 408h is shown in simplified form relative to the features
shown in FIGS. 2 and 3, but should be understood to include the
same components. Components that are the same for both processing
chambers 408g, 408h include RF electrode 215, insulator 230 and
diffuser 260. In the embodiment shown in FIG. 5, a remote plasma
source (RPS) 202 is a shared resource for both processing chambers
408g, 408h. RPS 202 receives input process gas(es) 155(2); further
input process gas(es) 155(1) may be mixed with plasma products from
RPS 202 and provided to processing chambers 408g and 408h, as
shown. Processing chambers 408g and 408h may receive further
process gas(es) 155(3) and 155(4), and may be respectively
energized by RF power supplies 510(1) and 510(2). Gases 155(3) and
155(4), and RF power supplies 510(1) and 510(2) are independently
controllable for processing chambers 408g and 408h. That is, it is
possible to provide different gas(es) and flow rates through the
gas connections, and/or operate one of RF power supplies 510(1) and
510(2) at a time, or operate power supplies 510(1) and 510(2) at
different power levels. The ability to control gases 155(3) and
155(4) and RF power supplies 510(1) and 510(2) independently is an
important feature for processing and chamber conditioning purposes,
as discussed further below.
[0052] FIG. 6 is a flowchart illustrating a method 600 for
assessing surface conditioning of one or more internal surfaces of
a plasma processing system. Method 600 begins with introducing one
or more plasma source gases within a plasma generation cavity of
the plasma system (610). The cavity is bounded at least in part by
the internal surfaces. For example, surface conditioning of
surfaces of face plate 225 (part of RF electrode 215) and diffuser
235 of plasma processing system 200, FIG. 2, can be assessed. In
this case, as shown in FIGS. 2 and 3, plasma generation cavity 240
is bounded at least in part by internal surfaces 226 and 236
(labeled only in FIG. 3). Plasma source gases 212 can be
introduced, as shown in FIG. 2. Method 600 proceeds to apply power
across electrodes of the plasma apparatus to ignite a plasma with
the plasma source gases within the plasma generation cavity (620).
For example, RF power may be provided across RF electrode 215
(including face plate 225) and diffuser 235, igniting plasma 245
within plasma generation cavity 240, as shown in FIGS. 2 and 3.
Method 600 further proceeds to capture optical emissions from the
plasma with an optical probe that is disposed adjacent the plasma
generation cavity (630). The optical probe is oriented such that
the captured optical emissions are not affected by interaction of
the plasma with a workpiece. An example of capturing the optical
emissions is receiving optical emissions 350 through optical window
310 into fiber optic 270, FIG. 3. Method 600 further proceeds to
monitor one or more emission peaks of the captured optical
emissions to assess conditioning of the one or more internal
surfaces (640). An example of monitoring one or more emission peaks
of the captured optical emissions is optical emission spectrometer
280, FIG. 2, analyzing the optical signal captured into fiber optic
270 to identify emission peaks, and utilizing information of the
emission peaks to assess conditioning of the surfaces.
[0053] In embodiments, the emission peak information may be
evaluated by a human. Alternatively, OES 280 and/or computer 290
may generate stability metrics from the information. For example, a
process sequence (hereinafter referred to as a "recipe," which
could be an "etch recipe," a "deposition recipe," a "conditioning
recipe" or other types, depending on the processing performed by
the process sequence) may include a step during which OES 280
measures optical emissions and creates information about emission
peaks. The information may include what peaks (e.g., spectral
wavelengths or wavelength bands) are detected, and/or intensity of
one or more detected emission peaks. The information may be further
processed by assessing trends such as changes in emission peak
intensity over recipe cycles, or by statistics such as calculating
mean, median, standard deviation and the like over groups of recipe
cycles.
[0054] FIGS. 7A and 7B illustrate emission peak information
obtained by using method 600 with apparatus like that shown in
FIGS. 2 and 3, for a plasma generated for a polysilicon etch
process. Optical emissions of a plasma were measured and displayed
using an OES 280 that automatically identifies known emission
peaks. In the examples shown in FIGS. 7A and 7B, peaks
corresponding to He, N.sub.2, H and F are labeled. The vertical
axis of each of FIGS. 7A and 7B is in arbitrary units (AU) of
signal intensity. Emission peak information such as intensities of
individual peaks, ratios of peak intensities, and other statistics
can be utilized to assess conditions of surfaces adjacent to the
plasma that is measured.
[0055] An example of assessing conditions of surfaces adjacent to a
plasma is illustrated in FIGS. 8A, 8B and 9. FIGS. 8A and 8B show
plots of emission peak intensities measured in a chamber generating
a plasma for a polysilicon etch process, over time, for a hydrogen
peak (FIG. 8A, data 700) and for fluorine peaks (FIG. 8B, data 710,
720). Both FIGS. 8A and 8B show data from the same plasma chamber
at the same time, starting after an equipment intervention was
performed, during which the chamber was open to atmospheric air for
a time. Conditioning cycles were run, and etch rate of a plasma
process on polysilicon was periodically measured. The time period
represented in FIGS. 8A and 8B is approximately 18 hours.
[0056] In FIG. 8A, it can be seen in data 700 that the hydrogen
peak intensity gradually increases over time. In FIG. 8B, it can be
seen in data 710 and 720 that the fluorine peak intensity increases
slightly within about the first two hours, but then remains about
constant.
[0057] FIG. 9 is a plot of selected ones of the hydrogen emission
peaks from FIG. 8A, and polysilicon etch rate measurements taken at
times corresponding to the selected hydrogen emission peaks. The
diamond shaped points in FIG. 9 are the H emission peak
intensities, correlated to the left hand vertical axis; the square
shaped points are the polysilicon etch rate measurements,
correlated to the right hand vertical axis; time is on the
horizontal axis. It can be seen that the polysilicon etch rate
varies similarly, over time, as the H emission peak intensities. A
trend analysis of etch rate against H emission peak intensity
revealed a correlation coefficient r.sup.2 of 0.97 for the
relationship of etch rate to H emission peak intensity. Therefore,
the H emission peak intensity strongly predicted etch rate, such
that stability in the H peak can be used as an indicator of
equipment stability. Reaction mechanisms underlying these
phenomena, and conditioning plasma recipes to improve etch process
stability are now explained.
[0058] Si Etch and Chamber Conditioning Chemistry and Recipes
[0059] A polysilicon (Si) etch process associated with the data in
FIGS. 7A, 7B, 8A, 8B and 9 proceeds according to the reaction:
2NF.sub.3+H.sub.2+Si(s).fwdarw.2HF+SiF.sub.4+N.sub.2 Reaction
(1)
wherein all of the species noted are in gas form except for solids
marked with (s). In reaction (1), polysilicon is the solid Si and
is provided as a film on workpiece 50, a semiconductor wafer;
NF.sub.3 and H.sub.2 are provided as gases and/or plasma products
(e.g., generated in plasma 245, see FIG. 2). Certain intermediate
steps are omitted in reaction (1); for example the plasma products
generated in plasma 245 include free H radicals.
[0060] Free H radicals in plasma 245 can adhere to yttria surfaces
of face plate 225 and diffuser 235. Although the full stoichiometry
of yttria is Y.sub.2O.sub.3, a yttria surface typically presents YO
at an outermost part of the surface, with which an H radical can
form a dangling bond:
H+YO.fwdarw.YOH Reaction (2)
[0061] FIG. 10A illustrates a yttria surface 750(1) that is devoid
of hydrogen, while FIG. 10B illustrates the same surface with a few
H radicals adhered to the surface through dangling bonds, forming
surface 750(2). Because surface 750(1) reacts with a fraction of H
radicals in plasma 245, the H radical concentration passing through
diffuser 235 is depleted. As more and more H radicals bond to the
surface to form surface 750(2), the rate of H radical depletion is
reduced, causing the H radical concentration reaching workpiece 50
to increase, leading to an etch rate increase as per reaction
(1).
[0062] While it may be possible in some cases to saturate a yttria
surface with hydrogen to stabilize etch rate, it can be very time
consuming to do so, and certain adverse process characteristics may
result. An alternative is to at least remove a portion of the
hydrogen and leave the surface at least substantially hydrogen
free, such that the etch rate is at least predictable. Free
fluorine radicals can scavenge the hydrogen, according to the
reaction:
F+YOH(s).fwdarw.YO(s)+HF Reaction (3)
[0063] Free F radicals can be supplied to perform reaction (3)
through a conditioning plasma step. In an embodiment, the
conditioning plasma step generates a plasma from NF.sub.3. While
other F-containing gases could be used for the conditioning step,
NF.sub.3 may be advantageously used if it is already plumbed into
the plasma processing equipment for a Si etch step. FIG. 10C
illustrates a yttria surface 750(3) reacting with free F radicals
to strip some of the H, as compared with yttria surface 750(2). To
reestablish etch rate stability in a chamber having excess H on
yttria surfaces, it is not necessary to remove all of the H. To
stabilize etch rate within a reasonable amount of time, it may be
sufficient to remove about as much H with a conditioning recipe, as
is added in an etch step. This can be done by performing the
conditioning plasma in between successive workpiece processing
steps. When a polysilicon etch process and the wafers being etched
are stable, a conditioning recipe can be run as a timed NF.sub.3
plasma step. It may also be desirable to monitor the H emission
peak during an NF.sub.3 plasma to determine a suitable time to stop
the plasma (e.g., based on the H emission peak falling to a
particular value). The H peak could be monitored during the
conditioning NF.sub.3 plasma step, or the H peak could be monitored
during the etch step and used to adjust one or more parameters of
the subsequent conditioning plasma step, such as gas flows,
pressure, RF power or time during the conditioning plasma step.
[0064] FIG. 11 is a flowchart that illustrates an etch recipe 800
that alternates etching on a workpiece, with a conditioning step.
Etch recipe 800 is generalized in that a variety of etch and
conditioning steps can be used, as now discussed.
[0065] Recipe 800 begins by loading a workpiece to be etched, in
step 810. An example of step 810 is loading a semiconductor wafer
with Si to be etched into plasma processing system 200, FIG. 2.
Next, in step 820 the etch is performed. An example of step 820 is
etching Si with NF.sub.3+H.sub.z, according to reaction (1) above.
During step 820, surfaces of the plasma processing system may be
degraded by plasma products and/or gases used for the etching. An
example of such degradation is H radicals forming dangling bonds to
yttria surfaces, according to reaction (2) above. An optional step
825 of monitoring an emission peak in the plasma using OES may be
performed concurrently with step 820, utilizing the apparatus
discussed above (see FIGS. 2 and 3). The emission peak information
may be used as an equipment monitor to confirm that the chamber
condition, and thus the etch rate, is stable from workpiece to
workpiece, and/or to adjust time of the conditioning step (step
840). In an example of step 825, H emission peak information is
monitored, recorded and/or used to determine when to stop later
step 840. After step 820, the workpiece may be unloaded in an
optional step 830; alternatively, step 830 may be omitted if the
processing described in step 840 will not impact the workpiece.
Omission of step 830 may lead to recipe 800 running a bit quicker
than if step 830 is included, because of the time typically
required to evacuate the process chamber for unloading, and to
reestablish gas flows for the plasma generated in step 840.
[0066] Next, in step 840 a conditioning plasma is performed. An
example of step 840 is conditioning the plasma generation chamber
with an NF.sub.3 plasma to remove H from the yttria surfaces,
according to reaction (3) above. An optional step 845 of monitoring
an emission peak in the plasma using OES may be performed
concurrently with step 840. An example of optional step 845 is
monitoring an H emission peak in the plasma using OES. The emission
peak information can be used to adjust time of step 840, and/or as
an equipment monitor to confirm that the chamber condition, and
thus the etch rate, is consistent after each repetition of recipe
800.
[0067] Considering recipe 800 in the context of FIGS. 4 and 5, it
is appreciated that when a pair of processing chambers 408 are
dedicated to similar processes, etch step 820 and/or conditioning
plasma step 840 could be adjusted specifically for each of the pair
of chambers 408, and this tailoring may be based on emission peak
monitoring. For example, recipe 800 could monitor an emission peak
during either etch step 820 or conditioning plasma step 840, and
adjust parameters such as gas flows, pressures, RF power and/or
time of conditioning step 840 across the two chambers to keep
performance of the two chambers tightly matched at etch step
820.
[0068] Si.sub.2N.sub.4 Etch and Chamber Conditioning Chemistry and
Recipes
[0069] An exemplary silicon nitride (Si.sub.3N.sub.4, sometimes
referred to herein simply as "nitride") etch process proceeds
according to the reaction:
4NF.sub.3+Si.sub.3N.sub.4.fwdarw.3SiF.sub.4+4N.sub.2 Reaction
(4)
[0070] In reaction (4), Si3N4 is provided as a film on workpiece
50, a semiconductor wafer; plasma products of NF.sub.3 are provided
to the workpiece (e.g., generated in plasma 245, see FIG. 2).
Certain intermediate steps are omitted in reaction (1); for example
the plasma products generated in plasma 245 include free F
radicals.
[0071] Free F radicals in plasma 245 can adhere to yttria surfaces
of face plate 225 and diffuser 235, forming dangling bonds:
F+YO.fwdarw.YOF Reaction (5)
[0072] FIG. 12A illustrates a yttria surface 900(1) with a few F
radicals adhered to the surface through dangling bonds. The F
radicals can desorb from the yttria surface during etching, and
cause degraded etch selectivity of the nitride etch with respect to
silicon dioxide (SiO.sub.2, sometimes referred to herein simply as
"oxide"). In at least some processing scenarios, nitride etches
need to be selective to nitride over oxide, that is, they should
etch nitride at a much higher rate than they etch oxide. Somewhat
analogously to the Si etch discussed above, the oxide etch rate
will climb, and thus the selectivity will degrade, as the F on the
chamber walls increases.
[0073] Another application of recipe 800 provides a way to
ameliorate this issue. Free H radicals can scavenge F from the
chamber walls, much like the reverse of reaction (3) above:
H+YOF(s).fwdarw.YO(s)+HF Reaction (6)
[0074] FIG. 12B illustrates yttria surface 900(2) undergoing
reaction (6). Like the Si etch and adsorbed H discussed above, it
may not be necessary to remove all of the F from yttria surface
900(2), but it may be helpful to scavenge F just down to a low
enough level that poor selectivity to oxide ceases to be an
issue.
[0075] Therefore, in one embodiment, recipe 800 can be run using
NF.sub.3 in etch step 820 to drive reaction (4), etching
Si.sub.3N.sub.4, and using a hydrogen-containing gas such as
NH.sub.3 and/or H.sub.2 in conditioning step 840, to generate free
H radicals to drive reaction (6). In this case, F emission peaks
could be monitored in step 845 to ensure consistency of the plasma
chamber condition at the end of step 840, before the next recipe
cycle when etch step 820 will be performed. It may also be possible
to run conditioning step 840 longer to drive adsorbed F to
extremely low levels if the next workpiece(s) to be processed would
benefit from an extremely high selectivity etch. Also, in this
embodiment, it may be possible to run recipe 800 without step 830,
if the workpiece would not be adversely affected by hydrogen plasma
products with traces of HF.
[0076] Chamber Conditioning Chemistry and Recipes--Adsorbed Oxygen
from Moisture
[0077] When plasma equipment is newly built or exposed to
atmospheric air during maintenance work, moisture can react with
fluorinated yttria surfaces such that extra oxygen adheres to such
surfaces. The oxygen adsorption process proceeds according to the
reaction:
2YOF+H.sub.2O.fwdarw.YO+YO.sub.2+2HF Reaction (7)
which is illustrated in FIG. 13A, showing surface 950(1) with
adsorbed fluorine, reacting to form YO.sub.2 in solid form, and HF
which is carried away in gas form. The extra O on the yttria
surface may react with processing plasmas and/or interfere with
intended reactions of such plasmas.
[0078] Like reducing adsorbed F, YO.sub.2 can be treated with a
hydrogen-containing gas such as NH.sub.3 and/or H.sub.2 to form a
plasma that removes the extra oxygen, leaving the yttria in its
native state. The plasma produces free H radicals as plasma
products, which react according to:
2H+YO.sub.2(s).fwdarw.YO(s)+H.sub.2O Reaction (8)
[0079] FIG. 13B shows surface 960(1) with an instance of YO.sub.2
in solid form. As shown in FIG. 13B, H radicals react with an
oxygen atom of the YO.sub.2 to form H.sub.2O, which is carried away
in vapor form from the resulting surface 960(2). Like the Si etch
case discussed above, an H emission peak could be monitored for
stability of plasma generation cavity surfaces, a constant H peak
signifying a stable YO surface. Also, the H containing plasma may
leave H adhered to YO surfaces, as discussed in connection with
FIG. 10B above. Therefore, depending on the processing that is
intended for the plasma processing equipment, the chamber could be
further conditioned with plasma generated from a
fluorine-containing gas (e.g., NF.sub.3) to reduce hydrogen that
may adhere to YO surfaces during the H radical treatment, as shown
in FIG. 10C. The conditioning treatment would amount to simply
running step 840 of recipe 800 (FIG. 11), optionally monitoring one
or more emission peak(s) with an optical emission spectrometer
(step 845) until the peaks are stable.
[0080] Having described several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Additionally, a number
of well-known processes and elements have not been described in
order to avoid unnecessarily obscuring the present invention.
Accordingly, the above description should not be taken as limiting
the scope of the invention.
[0081] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limits of that range is also specifically disclosed. Each
smaller range between any stated value or intervening value in a
stated range and any other stated or intervening value in that
stated range is encompassed. The upper and lower limits of these
smaller ranges may independently be included or excluded in the
range, and each range where either, neither or both limits are
included in the smaller ranges is also encompassed within the
invention, subject to any specifically excluded limit in the stated
range. Where the stated range includes one or both of the limits,
ranges excluding either or both of those included limits are also
included.
[0082] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a process" or "a recipe" includes a plurality of such processes
and recipes, reference to "the electrode" includes reference to one
or more electrodes and equivalents thereof known to those skilled
in the art, and so forth. Also, the words "comprise," "comprising,"
"include," "including," and "includes" when used in this
specification and in the following claims are intended to specify
the presence of stated features, integers, components, or steps,
but they do not preclude the presence or addition of one or more
other features, integers, components, steps, acts, or groups.
* * * * *